This felt like a vintage Michael Chang performance, so it was only appropriate he was sitting there with his arms leaning on the front-row railing, watching as his prized pupil echoed his style throughout another long and grueling U.S. Open afternoon that quickly turned to evening.

Chang began teaching Kei Nishikori in January, and Wednesday was a breakout performance for Japan’s best player, as the 24-year-old Nishikori took the court at Arthur Ashe Stadium and upset third-seeded Stan Wawrinka, 3-6, 7-5, 7-6 (7), 6-7 (5), 6-4.

The five-set win took 4 hours and 15 minutes, the second straight five-setter for the 10th-seeded Nishikori, who will take on No. 1 seed Novak Djokovic, who defeated Andy Murray in a hard-fought four-set night match.

It’s been a long couple days for Nishikori, who became the first of six players in U.S. Open history to win after having his previous match go past 2 a.m. As Monday night turned into Tuesday morning, Nishikori was battling against big-hitting Canadian Milos Raonic, the five-setter that finished at 2:26 a.m. — the exact ending time as the two previous latest matches.

With the win, the 24-year-old Nishikori also became the first Japanese man to reach the semifinals of a Grand Slam since 1918.

“Very honored to make the history,” Nishikori said. “A lot of Asian and Japanese fans come up — always fun to play here. I always enjoy [it].”

Nishikori left Japan at the age of 14 and went to Florida to play tennis at the famed IMG Academy in Bradenton. He already racked up two wins on Tour this year, but had to miss some time leading up to the Open after having a cyst removed from the big toe on his right foot.

Late in the fourth set, he coyly used a medical timeout to re-tape the toe, feigning an ankle injury, as ailments that existed previous to a match do not qualify as needing medical attention and the subsequent 10-minute delay.

But it allowed Nishikori to regroup, catch his breath, and show a commendable amount of resolve — much the way Chang did during his playing days. As an undersized Chinese-American, Chang endeared himself to New York tennis fans throughout the 1990s with his long and entertaining battles with more talented foes such as Pete Sampras, to whom he lost the 1996 U.S. Open final.

Now he has mentored Nishikori to do the same and beat back Wawrinka, the big hitter and reigning Australian Open champ.

“He’s telling me a lot of things to [do] to stay focused in the match and never get frustrated too much and always pump up yourself,” Nishikori said of Chang. “He told me congrats to win this battle, two in a row. But he also [said] it’s not done. Stay focused and try to recover these two days, and hopefully I have another good one next one.”